(1) Field of the Invention
This invention relates to additive combinations useful in lubricating compositions containing a major amount of an oil of lubricating viscosity and a minor amount of the additive combination. The lubricants are useful in two-cycle internal combustion engines. More particularly, the invention relates to additive compositions comprising a mixture of at least one alkyl phenol and at least one amino phenol, each having at least one hydrocarbon-based group of at least about 10 aliphatic carbon atoms. Since two-cycle engine oils are often combined with fuels before or during use, this invention also relates to two-cycle fuel-lubricant mixtures.
(2) Prior Art
A variety of phenolic compounds have been described which are useful as lubricant and fuel additives. Alkylated amino phenols have been described in U.S. Pat. No. 4,320,021 as being useful as additives for lubricants and fuels. Amino phenol and detergent/dispersant combinations have been described in U.S. Pat. No. 4,200,545 as being useful in lubricating compositions, particularly for two-cycle internal combustion engines and also as additives and lubricant-fuel mixtures for two-cycle engines. Hydrocarbon-substituted methylol phenols are described in U.S. Pat. No. 4,053,428 as useful in lubricants and fuels.
(3) General Background
Over the past several decades the use of spark-ignited two-cycle (two-stroke) internal combustion engines including rotary engines such as those of the Wankel type has steadily increased. They are presently found in power lawn mowers and other power-operated garden equipment, power chain saws, pumps, electrical generators, marine outboard engines, snowmobiles, motorcycles and the like.
The increasing use of two-cycle engines coupled with increasing severity of the conditions in which they have operated has led to an increasing demand for oils to adequately lubricate such engines. Among the problems associated with lubrication of two-cycle engines are piston ring sticking, rusting, lubrication failure of connecting rod and main bearings and the general formation on the engine's interior surfaces of carbon and varnish deposits. The formation of varnish is a particularly vexatious problem since the build-up of varnish on piston and cylinder walls is believed to ultimately result in ring sticking which leads to failure of the sealing function of piston rings. Such seal failure causes loss of cylinder compression which is particularly damaging in two-cycle engines because they depend on suction to draw the new fuel charge into the exhausted cylinder. Thus, ring sticking can lead to deterioration in engine performance and unnecessary consumption of fuel and/or lubricant. Spark plug fouling and engine port plugging problems also occur in two-cycle engines.
The unique problems and techniques associated with the lubrication of two-cycle engines has led to the recognition by those skilled in the art of two-cycle engine lubricants as a distinct lubricant type. See, for example, U.S. Pat. Nos. 3,085,975; 3,004,837; and 3,753,905.
The invention described herein is directed to minimizing these problems through the provision of effective additives for two-cycle engine oils and oil-fuel combinations which eliminate or reduce engine varnish deposits and piston ring seal failure.